On 17.09.20 10:46, Anshuman Khandual wrote:
> During memory hotplug process, the linear mapping should not be created for
> a given memory range if that would fall outside the maximum allowed linear
> range. Else it might cause memory corruption in the kernel virtual space.
>
> Maximum linear mapping region is [PAGE_OFFSET..(PAGE_END -1)] accommodating
> both its ends but excluding PAGE_END. Max physical range that can be mapped
> inside this linear mapping range, must also be derived from its end points.
>
> When CONFIG_ARM64_VA_BITS_52 is enabled, PAGE_OFFSET is computed with the
> assumption of 52 bits virtual address space. However, if the CPU does not
> support 52 bits, then it falls back using 48 bits instead and the PAGE_END
> is updated to reflect this using the vabits_actual. As for PAGE_OFFSET,
> bits [51..48] are ignored by the MMU and remain unchanged, even though the
> effective start address of linear map is now slightly different. Hence, to
> reliably check the physical address range mapped by the linear map, the
> start address should be calculated using vabits_actual. This ensures that
> arch_add_memory() validates memory hot add range for its potential linear
> mapping requirement, before creating it with __create_pgd_mapping().
>
> Cc: Catalin Marinas <catalin.mari...@arm.com>
> Cc: Will Deacon <w...@kernel.org>
> Cc: Mark Rutland <mark.rutl...@arm.com>
> Cc: Ard Biesheuvel <a...@kernel.org>
> Cc: Steven Price <steven.pr...@arm.com>
> Cc: Robin Murphy <robin.mur...@arm.com>
> Cc: David Hildenbrand <da...@redhat.com>
> Cc: Andrew Morton <a...@linux-foundation.org>
> Cc: linux-arm-ker...@lists.infradead.org
> Cc: linux-kernel@vger.kernel.org
> Fixes: 4ab215061554 ("arm64: Add memory hotplug support")
> Signed-off-by: Anshuman Khandual <anshuman.khand...@arm.com>
> ---
> arch/arm64/mm/mmu.c | 27 +++++++++++++++++++++++++++
> 1 file changed, 27 insertions(+)
>
> diff --git a/arch/arm64/mm/mmu.c b/arch/arm64/mm/mmu.c
> index 75df62fea1b6..d59ffabb9c84 100644
> --- a/arch/arm64/mm/mmu.c
> +++ b/arch/arm64/mm/mmu.c
> @@ -1433,11 +1433,38 @@ static void __remove_pgd_mapping(pgd_t *pgdir,
> unsigned long start, u64 size)
> free_empty_tables(start, end, PAGE_OFFSET, PAGE_END);
> }
>
> +static bool inside_linear_region(u64 start, u64 size)
> +{
> + /*
> + * Linear mapping region is the range [PAGE_OFFSET..(PAGE_END - 1)]
> + * accommodating both its ends but excluding PAGE_END. Max physical
> + * range which can be mapped inside this linear mapping range, must
> + * also be derived from its end points.
> + *
> + * With CONFIG_ARM64_VA_BITS_52 enabled, PAGE_OFFSET is defined with
> + * the assumption of 52 bits virtual address space. However, if the
> + * CPU does not support 52 bits, it falls back using 48 bits and the
> + * PAGE_END is updated to reflect this using the vabits_actual. As
> + * for PAGE_OFFSET, bits [51..48] are ignored by the MMU and remain
> + * unchanged, even though the effective start address of linear map
> + * is now slightly different. Hence, to reliably check the physical
> + * address range mapped by the linear map, the start address should
> + * be calculated using vabits_actual.
> + */
> + return ((start >= __pa(_PAGE_OFFSET(vabits_actual)))
> + && ((start + size) <= __pa(PAGE_END - 1)));
> +}
> +
> int arch_add_memory(int nid, u64 start, u64 size,
> struct mhp_params *params)
> {
> int ret, flags = 0;
>
> + if (!inside_linear_region(start, size)) {
> + pr_err("[%llx %llx] is outside linear mapping region\n", start,
> start + size);
> + return -EINVAL;
> + }
> +
> if (rodata_full || debug_pagealloc_enabled())
> flags = NO_BLOCK_MAPPINGS | NO_CONT_MAPPINGS;
>
>
Can we please provide a generic way to figure limits like that out,
especially, before calling add_memory() and friends?
We do have __add_pages()->check_hotplug_memory_addressable() where we
already check against MAX_PHYSMEM_BITS.
What I'd prefer is a way to get
1. Lower address limit we can use for add_memory() and friends
2. Upper address limit we can use for add_memory() and friends
something like
struct range memhp_get_addressable_range(void)
{
const u64 max_phys = (1ull << (MAX_PHYSMEM_BITS + 1)) - 1;
struct range range = arch_get_mappable_range();
if (range.start > max_phys) {
range.start = 0;
range.end = 0;
}
range.end = max_t(u64, range.end, max_phys);
return range;
}
That, we can use in check_hotplug_memory_addressable(), and also allow
add_memory*() users to make use of it.
--
Thanks,
David / dhildenb
